We reported the first homochiral metal halide ferroelectrics showing on/off switchable second-harmonic generation circular dichroism (SHG-CD) response. They exhibit strong SHG-CD with the anisotropy factor (g _SHG-CD) up to 1.28 and a 432F2 ferroelectric phase transition, enabling the unprecedented on/off switching of both SHG-CD and piezoelectric response between the SHG-CD/piezoelectric active and SHG-CD/piezoelectric inactive states.

Abstract

Homochiral ferroelectrics have attracted increasing attention in recent years because of their distinctive chiroptical effects in contrast to ordinary ferroelectrics. Moreover, they provide a great opportunity to show mathematically switchable matrix elements between nonzero and zero values in both second-order nonlinear optical susceptibility χ ⁽²⁾ and piezoelectric d matrices to realize the dual on/off switching of second-harmonic generation circular dichroism (SHG-CD) and piezoelectric responses, which, however, has never been reported. Herein, for the first time, we reported homochiral metal halide ferroelectrics (R-/S-BTA)₂CdBr₄ (BTA = 3-bromo-2-hydroxypropyltrimethylammonium), which exhibits a 432F2 ferroelectric phase transition at 362 K, accompanied by the switchable matrix elements between nonzero (for point group 2) and zero (for point group 432) values in both χ ⁽²⁾ and d matrices. They show strong SHG-CD effects with an anisotropy factor up to 1.28, far exceeding that of other chiral ferroelectrics. Notably, the 432F2 phase transition enables (R-/S-BTA)₂CdBr₄ to show the unprecedented dual on/off switching of SHG-CD and piezoelectric response between the SHG-CD/piezoelectric active state in the ferroelectric phase and SHG-CD/piezoelectric inactive state in the paraelectric phase. Our findings shed light on the exploration of mathematical double-matrix switchable chiral ferroelectrics with SHG-CD and piezoelectric response switching.